H1B approved; H4 denied due to not attending biometrics

You can file i539 with NPT option but you do not have much time to wait for its result.

USCIS may or may not approve it.

If they approve, everything will be hunky dory. But, if they deny, you would have already spent more than 180 days in ‘Unlawful presence’.

Some people have got success. You can read here: